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Super Bolt and Low pressure upgrades

This is only an idea - it is not supported by mathematics or physics only what I know - which is GCSE grade maths and physics.

Seeing as the superbolt is a lot lighter (1/3 or so) than a normal stock bolt - it shouldn't require as much force to get up to the required speed and force. I know the currect A.I.R. and RT valves are capable of being turned down to get more efficiency but they were not designed for this.

Maybe AGD you could re-engineer a valve so that it will work as efficiently as possible with a superbolt giving more shots (which i would love) and possibly a lower pressure (though not that needed it would be nicer to have a less harsh marker, and give me the chance to use higher grade paint).

Feel free to contradict, insult - congratulate or reward.

CiaranMail Me
"I have no need for a cup! I have balls of STEEL!!"
"Is it better to think you have freedom or know you have none?"

The weight of the bolt and the efficiency are not connected. You still need X amount of pressure to fire the ball at 300 fps. You also dont get more shots from low pressure and from what we see with the shocker and the impulse you get less.

Another idea - rather than having a superbolt with a delrin (sp?) sleeve, have one with a delrin core. Because as far as i can see most of the problems that are happening with the super bolt are as a result of it catching the spring, and the fact that it eventually wears out (though i dont think any ones had one that has worked long enough to replace the sleeve ).

Though the cross-section would look like - metal - delrin - metal - so that the bit that strikes the ball doesnt soften or have problems.

Benefit - in my head no wearing out of the delrin
- the sleeve wont catch the spring and come off.

lp v/s efficiency

I have a mag of which I am proud, but it needs a
super bolt and some plastic nubbins to help w/
ball breakage.

Low Pressure operation (lp) and efficiency do not
have to coexist, but it seems that each marker design
has a happy medium.

The Automag has to over come the force of the
return spring by applying force to the center rod of the
bolt. For the pressure to move the bolt to be lower, the
effective diameter of that rod need to be larger. That
could be accomplished with a larger diameter disc inside
the valve with a push rod to move the bolt.

The Autococker has several flavors, the 99 and before,
the 2000 and above, and the AKA. These all have different
valve areas and that makes them operate differently.

The 99's seem to get as low as 350 while efficiency rises.
When you get below that, your efficiency declines. The
2000's get to about 210 w/ an lp chamber, and the
AKA's get as low as 170 that I have seen. Below
these thresholds the efficiency degrades. Above these
it degrades.

The biggest advantage to lp is that the usable amount
of pressure in a tank is higher in an lp application. I can
get 1200 - 1400 shots from my mag from a 114/3000.
I can get 2000 - 2400 from the cocker on the same bottle.

Partly because below 800psi the mag starts to run lean
and the fails to operate. This could also be related to
the bottle in use. The cocker operates down to 200
psi before it becomes un-usable.

Both are great markers and I am not here to start any flame
war. I think that LP only applies to the point you have your
marker tuned to the point of maximum efficiency, then the
argument of lp breaks down.

I'll belive that statement when I see it with my own eyes. I concede though that it may be possible with a heavily modified Imp like one with an lpr driving the bolt and with a supershort dwell and operating upward of 250+psi. Then, and with some internal work the gun may be capable of that but out of the box I've never seen an Imp get anywhere near that number.

Originally posted by AGD The weight of the bolt and the efficiency are not connected. You still need X amount of pressure to fire the ball at 300 fps.

I have to disagree, the weight(mass) of the bolt must have some effect on efficiency.

It would be alot easier to explain useing a handful of useful formulae but i lack the math for it so I'm just gonna do my best without em.

The bolt has mass, the energy stored in the dump chamber is used to set that mass in motion, this energy is spent, the spring absorbs most of it then uses the absorbed energy to return the bolt to its origonal position where it strikes the valve disipating its remaining energy in the form of vibration or "kick", also a portion of the energy being applied to the bolt is absorbed by the paint ball causing the ball to move as well, probably matching the peak velocity of the bolt.
A bolt with less mass will achieve a greater velocity with the same amount of energy applied to it for the same distance, the paint being in contact with the lighter bolt will also achieve greater velocity.
An object traveling at 16 fps needs less energy added to it in order to achieve 300 fps than the same object traveling at 15 fps.

I know im splitting hairs but its always been my impression that thats what maximizing efficiency was all about, feel free to poke holes or maybe even supply the rest of the board with the relevent math involved with this.

I have to agree somewhat with "xatle". The more speed the ball gets before using any air source would definately incease efficency. How much efficiency? I'm not sure yet. Someone will have to sit down with their pen and paper and figure out the speed of the ball once the bolt is fully forward and the final velocity of the ball at the end of the barrel. Do it with different bolt weights and check the results. The lighter bolt should have slightly better efficiency and therefore be able to use slightly lower chamber pressure to achieve the same final velocity at the end of the barrel.

The difference may be so miniscule that it is of no consequence, but it would be interesting to know.

On the other side of the coin, would the increased speed that the lighter bolt could achieve, have a negative affect on the harshness of the mag on the paintball? Maybe the superbolt goes too fast and strikes the paintball with too much initial force. Has anyone thought of this angle?

Just a few thoughts.

Except for the Automag in front, its usually the man behind the equipment that counts.

"The weight of the bolt and the efficiency are not connected. You still need X amount of pressure to fire the ball at 300 fps."

The reason this is so because the pressure and volume that hits the ball is completely independant of the spring or mass of the bolt. Putting a softer spring or lighter bolt won't change that pressure at all.

The gas expands in the powertube pushing the bolt forward from say, 1ci to 2ci (no idea what the actual numbers are). Its new pressure doesn't matter if it pushed a big weight to expand or if it expanded effortlessly. Only thing that matters is the change in volume. And if you really wanted to test this. Fire a shot and chrono it. Take the bolt spring out. Fire another shot, see if the velocity jumps.

Actually...if anything, a lighter bolt/spring would drop velocity. Gas cools as it expands and cools faster the more rapidly it expands. Cooler gas = lower pressure = lower fps. But i think the change in rate of expansion is minimal for there to be any noticable change in cooling.

As for extra ball speed from a faster moving bolt, i think that is mostly negated by friction as soon as the ball enters the barrel. If the barrel was loose enough so that the ball could carry the extra velocity from the bolt movement, then you'd lose efficiency as more gas would escape around the ball.

i have no doubt whatsoever that removing the bolt spring would give you a noteable jump in velocity, an extra 30 or 40 fps wouldnt suprise me at all. not only would the bolt reach a much higher velocity but without the spring to return the bolt you get a complete dump from the chamber wich is in the neigborhood of an extra 50 psi(this isnt something that im willing to verify, if i hurt my mag it costs time and/or money to fix it, and that would suck).

how rapidly a gas expands doesnt change the total amount of cooling, only how steep the temperature spike is.

the ball should encounter the same barrel friction reguardless of what you use to push the ball.

im thinking that drilling out the center of the bolt plunger and filling it with epoxy or something along those lines might be a good plan to further reduce the weight of the bolt...hmmm... a titanium super bolt with an epoxy filled plunger...sounds pricey

If your body is really wierd, try showing it to people in the streets for money.-Hitchhikers Guide to the Galaxy, Tips for aliens in New York, Surviving

lp...

correct me if i'm wrong but as u lower the pressure it needs more air aka h.v.l.p. (high volume low pressure) if u dont use higher volume the gun would starve i think. so lp really does have its tradeoffs . if u think about it it will use more volume (the cubic inch part) if its using lower pressure(psi) i would also think if it need to use more air just at lower pressure then it would have a slower recharge rate because it need to put the higher volume of air into the gun... i think i probably made that as confusing as possible. tell me what u guys think

I would definately think the tension of the spring has an effect on velocity/effiency and the pressure in which the gun CAN operate at. Now the weight of the bolt is a different story.

First of all, we all know that a mag has a dump chamber pressure of about 400psi. We also know that there is roughly 60-80psi of air launching the ball out the barrel. Now tell me where the other 320-340psi goes....most of it must be used to push the bolt forward against the spring.

These are just thoughts here and have no fact behind them. It would seem that a weaker bolt spring would take less pressure to push the bolt forward. Let's say you went with a spring about 5x weaker, you could run the gun between 120-200psi. The way I would do this would be to remove all of the internals of the valve except for the on/off assembly. Replace the back reg with a hollow air chamber to store more available air. On the retro valve, you would have to plug the little hole on the side that goes into the piston assembly, so air doesn't leak out. Some of the air passageways would maybe need to be enlarged. A good lp reg with great flow capabiltity's would also be needed. Now your velocity is controled by your input pressure. 120psi may give you 200 fps. 190psi may give you 280's.

I cool test to do is to remove the brass reg seat thingy that is held in place by the back reg. Next have an accurate way to measure input pressure. Start out around 300 psi and chrono the gun. Now put 350 or 400psi into the gun and re-chrono. See what kind of input pressure it takes to get to a desired velocity and that pressure will be the working pressure of your valve(at a specific velocity of course). If you try to rapid fire without this piece you will have major shootdown.

Sure if you go with a lighter bolt spring your bolt won't return as fast, but if it came down to getting a couple hundred extra shots per tank and less barrel breaks(assuming this would slow down bolt speed making it easier on the next ball in the stack), vs being able to shoot 18sps, I know what I would favor, do you?

This would be interesting to test out. I may have to go remove my bolt spring and the brass reg seat thing, put 120psi into the gun and see what it chrono's in at. If anyone else tries this, let us know back here.

Missing Pressure

The peak behind-ball pressure during a firing cycle is around 60 psi. The peak pressure occurs early in the firing cycle, when the ball is darn close to the bolt. To drop the chamber pressure from 400 psi to 60 psi simply on a p1*v1=p2*v2 basis would require the total volume to increase by at least a factor of six. This simply does not happen between the chamber, power tube, bolt, and space behind the ball until the ball is quite a distance down the barrel. Thus, pressure drop is not purely a pressure-volume effect.

I believe the bolt, return spring, and power tube act as a sort of regulator, limiting the flow of gas from the chamber to behind the ball. This in turn limits the peak pressure that can be generated during firing, and increases the time required to achieve this pressure as compared to a knock-open type of valve system. I believe somewhere in the following thread Tom stated that the Matrix and the Automag take slightly longer than most other markers to reach their peak behind-ball pressure.

An interesting experiment would be to test a Mag's behind-ball pressure for different bolt return spring strengths. Stronger springs should take longer to reach peak pressure, and that peak pressure should be lower. Without having a barrel with a pressure sensor in it, one might be able to perform the test by observing the average exit velocity of paintballs fired from the Mag as one uses bolt return springs of different strengths.

Hmmpf!

Sheesh. I've heard a lot of stuff, but some of this takes the cake. Surely Kilaueakid is pulling our leg - and trying to see if anyone is fool enough to hose his mag!

There's no way the bolt/power tube is acting like a regulator. To do that the bolt would have to sit close to it rearmost position, the only place an air-tight fit occurs. In a closed system, the change in pressure will only result from change in volume, or change in temperature. The strength of the spring or weight of the bolt has no effect on the pressure other than some small amount of loss due to temperature.

Where does the 350 psi go? Well, to start with a lot of it goes right where Bad Dave said it goes. Expand the chamber to include the powertube and bolt and the pressure goes way down. But its not enough you say? No its not. Think about the relationship of the bolt, the bolt plunger (not sure if that's the right term) and the power tube when the bolt is fully extended. There is a HUGE air space between the power tube and the body, and the air flow is open to that space.

But that STILL isn't where ALL of it goes. Who ever said that the pressure in the entire chamber/power tube/bolt system is evenly distributed. Sure, if you leave it long enough it will be, but you can rest assured that a pressure wave runs down the powertube, bounces around as it tries to avoid the bolt plunger, and then heads down the bolt to find the ball. By the time the REST of the air pressure gets there, the ball has begun moving down the barrel, further enlarging the volume so the bulk of the air doesn't seem to produce as much pressure at the site of the ball.

The weight of the bolt and stiffness of the spring will only affect the speed of the bolt. That might have a small effect on the inital movement of the ball, but apparently not enough to be noticed. In truth, there must be SOME effect on energy transfer, but the efficiency effect pales in comparison to the blast of air out the barrel after the ball leaves. In other words, the efficiency might work out differently in theory, but probably doesn't make much useful difference in practise.

I'll close by saying I haven't tested all of this, but I tend to trust what Tom says - if it doesn't affect efficiency that is most likely why.

Bjjb99....just out of curiosity, you say the valve would need to be increased by a factor of 6x. If that is the case, than how do some of these lp guns do it without having a dump chamber the size of pop can?

Another thing that is apparent on the mag is that when chamber volume doubles, the operating pressure is NOT cut in half. It will go down, but is not a 50/50 relationship.

I guess I am just a little confused on this subject, to me it would seem that a bolt return spring with much less tension would not need 400psi to get the bolt past the end of the powertube tip to release the 60-80psi burst on the ball. Maybe it would only need 200psi? What is the stock spring tension...35 lbs? what if the spring were 10 lbs tension? Sorry for any confusion and don't go hacking up your guns!!! Interesting subject though guys!

It only takes about 50-60 psi to get the bolt out past the end of the power tube. That is why the residual pressure in the dump chamber of the mag is about 50 psi. Below this pressure the spring is able to push the bolt back against the pressure.

As for the pressure vs volume, a lower pressure and higher volume reduces efficency because the ball cannot be accelerated to a high velocity nearly as quickly. The acceleration lasts longer, the pressure variance from beginning of the barrel to end of barrel is less, but the residual pressure in the barrel as the ball exits is higher. This "exhaust" out the end of the barrel is wasted and the effect of the air flow out the end causes a negative pressure in the barrel as well. The only place that the low pressure guns gain some of the efficiency back is in the fact that they can use more of the gas available in the bottle.

An example would be:

1) A 400psi mag set to use a 800psi input gets 800 shots off a 3000psi bottle. It equates to 2.75 psi per ball fired.

2) A low pressure gun set to 200psi input pressure gets 900 shots off a 3000psi bottle. It equates to 3.1 psi per ball fired.

The mag operates at about 60 psi max in the barrel as the ball is fired. This is achieved as the 400 psi is forced through a smaller ventrical called the power tube. This acts as a restrictor. As the air exits the other end of the tube into the barrel it pushes the ball forward causing the barrel volume to increase. Due to the increasing volume and the restricted flow, the pressure never gets above 60.

As for low pressure guns having a dump chamber the size of a pop can. The mag has a dump chamber of only .55 cubic inches. Many low pressure guns have dump chambers in excess of 2 cubic inches. Thats about 4 times the size.

A very, very long post...

FatMan wrote:
> There's no way the bolt/power tube is
> acting like a regulator. To do that the
> bolt would have to sit close to it
> rearmost position, the only place an
> air-tight fit occurs.

Regulators do not have to be air tight to do their job in a flow through system. All they must do is restrict the flow sufficiently, causing the downstream pressure to drop. This can be demonstrated with a garden hose and a couple of valves. Since the plunger in the center of the Mag's bolt does not completely exit the powertube, the bolt plunger restricts airflow. The amount of restriction is dependent on the location of the plunger relative to the power tube tip. This position is controlled by the strength of the return spring, the diameter of the bolt plunger, and the differential pressure in front of and behind the bolt. Hence, the bolt and return spring act as a regulator. The spring limits the travel of the bolt, which determines how much the airflow through the powertube is restricted.

> In a closed system, the change in
> pressure will only result from change
> in volume, or change in temperature.

Agreed, in the ideal gas case which is what we're assuming.

> The strength of the spring or weight of
> the bolt has no effect on the pressure
> other than some small amount of loss
> due to temperature.

I believe you're likely correct with regards to the bolt weight, but I'm not so sure about your claims regarding the spring. The only way to find out for sure would be to perform a test using different spring strengths.

> Where does the 350 psi go? Well, to
> start with a lot of it goes right where
> Bad Dave said it goes. Expand the
> chamber to include the powertube and
> bolt and the pressure goes way down.
> But its not enough you say? No its not.
> Think about the relationship of the
> bolt, the bolt plunger (not sure if
> that's the right term) and the power
> tube when the bolt is fully extended.
> There is a HUGE air space between the
> power tube and the body, and the air
> flow is open to that space.

The dump chamber in a Mag is around 0.55 cubic inches in volume, as stated in the following thread:

I do not have my Mag in front of me, so I'm working from memory here. The outer diameter of the powertube is approximately 0.5 inches. The tube is approximately 1.5 inches long. The inner diameter of the powertube is approximately 0.25 inches. The interior volume of the tube would therefore be around 0.07 cubic inches.

The bolt consists of a cylindrical volume with a piston in the middle. The piston diameter is approximately 0.25 inches, and it's about 1.5 inches long. The inner diameter of the bolt is around 0.5 inches, and again, is around 1.5 inches long. The total volume inside the bolt (minus the portion occupied by the piston) would therefore be around 0.22 cubic inches.

I don't necessarily agree with your statement that the air can flow out of the powertube and back behind the bolt. It seems to me that the bolt plunger remains in the powertube; thus, the rear of the bolt itself remains around the exterior of the powertube, restricting airflow into the space behind the bolt. However, I'll assume that you're correct for this calculation.

The inner diameter of the Mag's body is around 1 inch. The region between the dump chamber and the bolt's rear face when the bolt is in its forward position is about 1.5 inches long. The total volume of this space (minus the portion occupied by the powertube) would therefore be around 0.88 cubic inches.

0.88 + 0.22 + 0.07 = 1.17 cubic inches.
Including the dump chamber volume brings this up to 1.72 cubic inches, a factor of right around 3 increase in volume. By your argument (and my estimates of sizes), the behind ball pressure would be around 130 psi. We've still got a factor of two somewhere that isn't taken care of yet. Even if we increase the lengths of the powertube, bolt, etc to 2 inches, we're still significantly on the low side in terms of required volume.

> But that STILL isn't where ALL of it
> goes. Who ever said that the pressure
> in the entire chamber/power tube/bolt
> system is evenly distributed. Sure, if
> you leave it long enough it will be,
> but you can rest assured that a
> pressure wave runs down the powertube,
> bounces around as it tries to avoid the
> bolt plunger, and then heads down the
> bolt to find the ball. By the time the
> REST of the air pressure gets there,
> the ball has begun moving down the
> barrel, further enlarging the volume so
> the bulk of the air doesn't seem to
> produce as much pressure at the site of
> the ball.

In the thread whose URL I listed above, Tom posted a picture of an Angel's pressure curve, showing when the ball began its motion relative to the peak pressure in the barrel. He has stated that the ball begins its motion pretty darn close to the top of the pressure curve, regardless of the type of gun being fired.

To reach the total volume (chamber + powertube + bolt + space behind the bolt + volume between bolt and ball somewhere down the barrel) which would drop the pressure down to around 60 psi, the ball would have to be around 5 inches down the barrel. This conflicts with the above paragraph in terms of when the peak pressure occurs.

The only explanation I can come up with is the plunger is restricting the airflow through the powertube, thus limiting the peak pressure. Since the bolt return spring strength is what is limiting bolt travel, we've got a regulator of sorts.

kilaueakid wrote:
> Bjjb99....just out of curiosity, you
> say the valve would need to be
> increased by a factor of 6x. If that is
> the case, than how do some of these lp
> guns do it without having a dump
> chamber the size of pop can?

An interesting question... here's my take on it. Many lp guns operate at a lower chamber pressure than the Mag (250 psi versus the Mag's 400 or so). Tom has stated that the Mag has one of the lowest behind-ball pressures in the paintgun world. His plot of the Angel's pressure curve shows a peak behind-ball pressure of around 100 psi for that gun. If you start with 250 psi and only drop to 100, you don't need nearly as large a volume increase as you would going from 400 psi down to 60. Thus, the lp guns that start with a lower operating pressure have no need for soda can sized volumes into which the pressure can expand. Athomas has already stated that initial chamber sizes in lp guns can be 4 times that of a Mag.

> Another thing that is apparent on the
> mag is that when chamber volume
> doubles, the operating pressure is NOT
> cut in half. It will go down, but is
> not a 50/50 relationship.

I'm pretty sure I disagree with this statement. Can you point me to a reference which explains what you're saying? Maybe it's the way it's worded, but it sounds like you're darn close to violating a thermodynamic law or two.

Athomas wrote:
> The mag operates at about 60 psi max in
> the barrel as the ball is fired. This
> is achieved as the 400 psi is forced
> through a smaller ventrical called the
> power tube. This acts as a restrictor.
> As the air exits the other end of the
> tube into the barrel it pushes the ball
> forward causing the barrel volume to
> increase. Due to the increasing volume
> and the restricted flow, the pressure
> never gets above 60.

That's a good concise description of the Mag's behavior. The only thing I might add is that the bolt plunger does not completely exit the powertube, further restricting the airflow.

the pressure at which the bolt is moved and the pressure that is released firing the ball are the same in the automag. To be act gently on the paint, you want the bolt to run at a lower pressure. if you want to lower bolt pressure, your valve pressure(burst of air firing ball) is lowered too. this means that your automag is going to have decreasing efficiency when you lower the pressure. if you were to have a duel regulator in the AIR assembly, one that controls bolt pressure and one that controls valve pressure then you could possibly reduce pressure. this is most likely not feasible with the current valve assebly design. you would have to create a new gun. low pressure reduces efficiency. i get about 1250 shots per 20oz. with my impulse. i'd say that's respectable and i run at about 150psi with no lpr.

Hmm, something funny.

bjjb99:

OK, well I'm not really clear on all of that. My definition of a regulator is not the same as yours. The plunger (among other things) limits the flow of air out of the dump chamber. I had accounted for that. The spring isn't going to have much effect on that, as the bolt will travel its length in any (working) case and the only real difference would be plunger in the tube versus plunger out of the tube. The airflow is restricted by geometry, not spring tension.

The dimensions you mentioned sound OK. The "pressure reduction" sounds OK. I wasn't expecting more than that (which is what I meant when I said "that STILL isn't where ALL of it goes").

What you missed is the part that comes after that. The bolt is only open for a few milliseconds. When the bolt closes again there is still pressure in the chamber. In other words not all of the pressure in the dump chamber is vented to the ball and out of the barrel.

So, I think we're saying almost the same thing, only I don't call that a regulator, I call it restricting air flow - and I don't believe spring tension has much of an effect on it. Some, but not enough to really make a big difference on efficiency. I also think you'll find that the plunger DOES exit the power tube for all practical purposes (the tip of the plunger may not extend past the tip of the tube, but it extends well past the beginning of the flared portion of the tip).

Call it what you want - that's fine with me, but that still doesn't add up to bolt mass or spring tension having a significant effect on efficiency - which I think was the point of the discussion.

reducing bolt speed is easy, all you need to do is reduce the i.d. of the power tube and o.d of the bolt plunger, reduce the area of the bolt that is in contact with the pressure in the dump chamber and you reduce the total force felt by the bolt. the smaller power tube would also further restrict air flow, reducing the peak pressure behind the ball and increasing the amount of time needed to dump the chamber.
this may or may not be an improvement, but it wouldnt be too hard to experiment, just need a bolt with a removeable plunger and a handfull of different sizes of plungers and power tube assembly's, well, sounds easy anyway...

The thinking is on track here. Yes you can slow the bolt speed by reducing the size of the power tube but then it is too small to flow all the air needed fast enough. The other problem is that orings do not come in small enough size increments to experirment. You just cant say you want a .200 power tube and get an oring for it.

FatMan wrote:
> OK, well I'm not really clear on all of
> that. My definition of a regulator is
> not the same as yours.

Heck, for all I know, I may be calling it a regulator when it really should be called a restrictor. Perhaps a restrictor is simply a dynamic form of a static pressure regulator.

> The plunger (among other things) limits
> the flow of air out of the dump
> chamber. I had accounted for that. The
> spring isn't going to have much effect
> on that, as the bolt will travel its
> length in any (working) case and the
> only real difference would be plunger
> in the tube versus plunger out of the
> tube. The airflow is restricted by
> geometry, not spring tension.

In a properly functioning Mag, the bolt does not "bottom out" against the spring. See the following thread for reference:

The bolt return spring is not fully compressed during a normal firing of the gun. The distance the bolt travels is limited by the strength of this spring. Put a very strong spring in there, and the pressure behind the bolt plunger can't overcome the spring force. Remove the spring, and the bolt will travel its full length. Spring strengths in between these two extremes will result in different amounts of bolt travel, particularly when air begins to work its way past the plunger and powertube tip. I agree the airflow is restricted by geometry; that geometry is determined by the force of the spring and the differential pressures on either side of the bolt. In such a complex interface as the powertube tip and bolt plunger, a few hundredths of an inch in either direction can significantly change the gas flow rate, and therefore the behind-ball pressure curve will be affected.

> What you missed is the part that comes
> after that. The bolt is only open for a
> few milliseconds. When the bolt closes
> again there is still pressure in the
> chamber. In other words not all of the
> pressure in the dump chamber is vented
> to the ball and out of the barrel.

Absolutely true. That's why I included the chamber volume in my calculation. The final pressure in the dump chamber is around 50-60 psi, which seems to indicate that the chamber gets sealed shortly after the behind-ball pressure reaches its peak.

> So, I think we're saying almost the
> same thing, only I don't call that a
> regulator, I call it restricting air
> flow

Sounds reasonable enough to me. I've been working under the premise that one can regulate pressure dynamically by restricting flow.

> and I don't believe spring tension has
> much of an effect on it. Some, but not
> enough to really make a big difference
> on efficiency.

I agree with you here. My original post was an effort to explain to kilaueakid where "the other 320-340psi goes". I am making no claim regarding efficiency, though it would be interesting to see how a Mag with an operating chamber pressure of 150 psi compares to a standard Mag.

I still think it would be an worthwhile experiment to see what the behind-ball pressure is during firing if one uses bolt return springs of different strengths. I'm guessing that the behind-ball pressure will be lower for stronger springs and higher for weaker springs, simply because of the flow restriction/regulation caused by the relative positions of the bolt plunger and powertube tip.

BJJB

kilaueakid, when I searched for it, I was not able to find a post describing the chamber volume for the aluminum valves. I believe I did see the 300 psi chamber pressure mentioned, though.

OK

In a properly functioning Mag, the bolt does not "bottom out" against
the spring. See the following thread for reference:

Agreed. I've read the thread several times. I don't equate not
bottoming out with not clearing the power tube tip

The bolt return spring is not fully compressed during a normal firing of
the gun. The distance the bolt travels is limited by the strength of
this spring. Put a very strong spring in there, and the pressure behind
the bolt plunger can't overcome the spring force. Remove the spring,
and the bolt will travel its full length. Spring strengths in between
these two extremes will result in different amounts of bolt travel,
particularly when air begins to work its way past the plunger and
powertube tip. I agree the airflow is restricted by geometry; that
geometry is determined by the force of the spring and the differential
pressures on either side of the bolt. In such a complex interface as
the powertube tip and bolt plunger, a few hundredths of an inch in
either direction can significantly change the gas flow rate, and
therefore the behind-ball pressure curve will be affected.

I'm with you on all that, except maybe the last statement. On that I'd
have to say I just don't know. A significantly stronger spring would
prevent the plunger fully exiting, and the gun wouldn't work right. A
significantly weaker spring would let the bolt bottom out and it might
work, but would have a lot more recoil. Small variations in spring
strenth I doubt have much effect on pressure to the ball. Maybe some,
but then you adjust the chamber pressure and that goes away.

Absolutely true. That's why I included the chamber volume in my
calculation. The final pressure in the dump chamber is around 50-60
psi, which seems to indicate that the chamber gets sealed shortly after
the behind-ball pressure reaches its peak.

Again I doubt that's true. I will say very loudly I'm guessing here,
but I'd bet the bolt doesn't return until after the ball is out of the
barrel. The ball is gone in about 6ms, and I have heard figures like
10ms for bolt return, though I'm not sure those are correct (Tom, do you
want to clue is in or this, or do you prefer to sit back and just watch
us stab in the dark? :-) ). I think the flow restricting issues are a
combination of the chamber to power tube to bolt system, and that the
exact position of the bolt (governed by the spring) doesn't have much to
do with pressure that meets the ball, provided the bolt at least goes to
a position within tolerance.

I agree with you here. My original post was an effort to explain to
kilaueakid where "the other 320-340psi goes". I am making no claim
regarding efficiency, though it would be interesting to see how a Mag
with an operating chamber pressure of 150 psi compares to a standard
Mag.

I still think it would be an worthwhile experiment to see what the
behind-ball pressure is during firing if one uses bolt return springs of
different strengths. I'm guessing that the behind-ball pressure will be
lower for stronger springs and higher for weaker springs, simply because
of the flow restriction/regulation caused by the relative positions of
the bolt plunger and powertube tip.

Yeah, like I said - its not a really fundamental argument, just friendly
hashing! I'm all for experiments, but for now I'll hold to my
prediction that the spring tension isn't a major factor in the design.
But, I could be all wrong.

Oh, and its sure is lot more fun to discuss this with you than someone
without a clue! You've made me think about what I'm saying!

FatMan wrote:
>
> Agreed. I've read the thread several
> times. I don't equate not bottoming out
> with not clearing the power tube tip

That makes some sense, given that the bolt plunger is somewhat recessed inside the bolt. I'm going to have to take some accurate depth measurements for the Mag's body and compare them to the bolt length, the spring thickness when fully compressed, the power tube length, and the length of that bolt plunger. We should be able to determine how far out of the power tube tip the plunger travels in a "bottoming out" condition. That would at least put some geometrical limit on the airflow restriction.

Now where did I put my calipers...

> Yeah, like I said - its not a really
> fundamental argument, just friendly
> hashing! I'm all for experiments, but
> for now I'll hold to my prediction that
> the spring tension isn't a major factor
> in the design.

The thing that bugs me all the time is that there are all these really interesting puzzles out there, and when I come up with an experiment to take a look at one of 'em, I end up not having the resources to perform the test! I really want to stick a pressure sensor (or a series of 'em) in a barrel and fire some paint, but I lack the N-thousand dollars necessary for an accurate and precise testing system! Grrrr.

Oh, for anyone reading this, cash donations are accepted, but they're not tax-deductible.

> But, I could be all wrong.

Who knows... we both could be wrong and it's really just a bunch of magic elves doing the work.

> Oh, and its sure is lot more fun to
> discuss this with you than someone
> without a clue! You've made me think
> about what I'm saying!

It's always good to explore a topic with someone who makes me exercise my brain. If I ever get a testing rig set up, I'll be posting my results .

Now THERE'S an idea!

Now why didn't I think of that! If someone would just put up the funding we could put all of this to rest! bjjb99 can do the physical experiments, I can do the computational model.

I've got some experts in fluid dynamics here, and we've discussed several models of the Mag. All I need is a graduate student for the summer to get the coding done and we'd have something. Including overhead and all we'd be looking at $10K - which is REALLY cheap by industry standards if you think about it. I have the machine to do it on (500 1GHz P3 cpus) and the people with the know how. Just need the cash to pay the grad student.

Tom, you want to invest in a little research?

Now, if there was some way that the federal government would get interested in this ... hmmm ... NASA? ... DOE? ... DOD? Maybe. But they'd want to model REAL guns.